At least one example embodiment of the inventive concepts relates to a memory device, and more particularly, to a nonvolatile memory device and a memory system including the nonvolatile memory device.
Memory devices are used to store data, and may be divided into volatile memory devices and nonvolatile memory devices. Volatile memory devices lose their stored data when power supply is interrupted. However, nonvolatile memory devices retain data even when power supply is interrupted.
A flash memory system, which is an example of the nonvolatile memory device, is widely used in, for example, a Universal Serial Bus (USB) drive, a digital camera, a mobile phone, a smartphone, a tablet, a personal computer (PC), a memory card or a solid state drive (SSD).
Threshold voltages of multiple programmed memory cells included in a nonvolatile memory device may change for various reasons such as retention, floating gate coupling, or charge loss over time. Such changes may degrade reliability of read data. Changes in threshold voltages for various reasons as described above will be referred to as ‘degradation’ below.